1. Field of Invention
The invention relates to solvent extractors commonly used for the removal of oils, fats and waxes from solid material such as oil-bearing seeds, hops, lignite, rice bran, etc. The solvent will depend on the component to be extracted. Hexane, alcohol, blend of alcohol and toluene, chlorinated solvent are typical. Water may be used where it is a satisfactory solvent for removing the extractable component, e.g. the extraction of proteins from meal. Generally, the present invention relates to extractors for extracting a component that can be soaked or leached out of a solid material.
More particularly, the present extractor is designed for use with material which does not lend itself to extraction by the so-called percolation method. Percolation extractors are dependent on granular material or material that has voids permitting the solvent or the leaching media to drain through the solids. Some materials are too finely divided resulting in a very dense bed that does not lend itself to the percolation or the transfer of solvents from the surface on through the bed of the material. This may also occur where the material is too high in moisture or too high in fat. Examples of materials with which the present extractor is designed for use are finely divided lignite (for Montan wax extraction), rice bran, hops, animal fat where the fat content of the meat scrap would be in excess of about 40%, etc. Oil seeds, for example, may be processed to screen the coarser material which may be processed through a conventional percolation extractor and the fine material processed through the present immersion extractor to increase the overall oil recovery and capacity of the plant. Similarly, in the case of lignite, the coarser material obtained by screening may be processed through a percolation extractor and the fine material would be processed in the present immersion extractor.
2. Description of Prior Art
Solvent immersion extractors are shown in U.S. Pat. Nos. 1,826,945; 2,227,605; and 2,703,274.
Of the three patents noted, the most pertinent is Swallen et al, U.S. Pat. No. 2,227,605, disclosing an apparatus for extracting zein (the alcohol soluble constituent of corn protein) from gluten meal using an alcoholic solvent and a series of settling vessels for the solvent through which the meal is moved by a series of conveyors. Each of the settling vessels is preceded by a mixing vessel having a rotating agitator for mixing the solid material with the solvent, the arrangement being that the mixture of solids and solvent thus made into a flowable mixture overflows a weir separating the mixing and settling chambers for deposit in the settling chamber. A drag conveyor is used to move the solid materials through the settling chamber and up and over an inclined bottom wall containing a screen for permitting solvent to drain back into the chamber. Each of the chambers has its own conveyor which returns overhead to re-enter at the opposite side of the chamber in an endless configuration. One of the disadvantages of the Swallen structure is that the drag conveyor moves up through the settling chamber on an inclined path and as it does so disturbs and agitates the surface of the miscella (alcohol and dissolved zein). A solvent immersion extractor depends upon the solid portion being heavier than the miscella so that it will settle to the bottom of the settling chamber and at the same time the miscella will float to the top of the solvent bath from where it is decanted. It is, accordingly, most important and forms a feature of the present invention that the surface from which the miscella is decanted is both clean and quiescent. Swallen et al depends on the obtaining of a homogenous mix overflowing the weir of the mixing chamber--a system which would not work with lignite where the heavy particles, including sand, would accumulate on the bottom.